10th Asian Regional Conference of IAEG (2015)
Erosion Zone Arround Upper Cisokan Dam, West Java, Indonesia
Ichsan ALFAN(1), Novian TRIANDANU(1), and Dicky MUSLIM(2)
(1)Faculty Geology, Padjadjaran University, Jatinangor 45363, Indonesia
E-mail :[email protected]
(2)Postgraduate Program of Geology University of Padjadjaran, Bandung 40115, Indonesia
Abstract
Study area is located in Cisokan drainage area, Bandung, West Java Province,
Indonesia. Potential disaster that may occur around the study area is soil erosion and in
this reaserch area upper Cisokan Dam is under development therefore the study of soil
erosion is necessary. The objective is to characterize and to determine erosion zone that
may affect to the study area. Some methods are used in this research such as desk study,
field work and laboratory analysis. Desk studies consist of morphography analysis using
Digital Elevation Model. Field works consist of Outcrops analysis, Survey of landuse
area and measurement of actual erosion. Lab analysis consist correlation between
geological factor, landuse and actual erosion to make deliniation for erosion zone.
Result of this study shows that the lithology of this area is dominant by Miocene
Sandstone which is erodible. Slope, elevation, geological structure, ground water
facies , soil characteristicsand high rainfall which are developed in the study area are
affects to erosion level. From this reasearch we can conclude that elevation in the
research area has 400 – 1025 above sea level. Slope zonation in this study area is
devidedinto two zones, namely steep and very steep slope.Steep slope occupy in 55%
west study area. Very steep slope occupy in 65 % east study area. Opening land and
vegetasion of this area increase erosion level which endanger Upper Cisokan Dam
developement around the research area.
Keyword: Soil Erosion, Upper Cisokan Dam, Indonesia, Geohazard
1. Introduction
Erosional process in earth happens gradually
and caused by some water and wind activity.
Erosional process can be divided into two,
geological erosion or normal erosion and
accelerated erosion.
Normal erosion occurs naturally and
continuously, forming topographic landform and
producing sediment material. Water, wind and
gravity are the main transport media.
Accelerated erosion in tropical region
commonly caused by surface water activity.
Water is the main transport media and play
important role. Splash erosion, sheet runoff,
interill erosion, rill & gully erosion, riverine
erosion, wave action, foreshore erosion or beach
erosion, and piping or tunnel erosion are kinds of
water mediated erosion.
Soil erosion is the common geological hazard
in tropical region and has major impact in area
where it occurs. High rainfall intensity, steeply
slope, and vegetation loss due to terrain utilization
are factors that modified terrain characteristics in
study area, forming sloping morphology that
potentially act as gliding plane and may cause
landslide, damaging village around, infrastructure
and material loss.
The building of Upper Cisokan Dam located
in study area. Power plant that supply 1040
Megawatt for Java-Bali Region is under
development. Potential disaster that may occur
around this area is soil erosion and slope stability
problem and considering in development of
Upper Cisokan Dam, this research become
necessary.
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10th Asian Regional Conference of IAEG (2015)
Project Area
West Java Province
mode and when collaps can performing black
start..
Upper Cisokan catchment area is about
10,5 km2, fluctuation of water level in normal
elevationl +777,5 masl and in the lowest
condition at elevation +777,5 masl, Lower dam
has 98,00 m concerete gravity, top Dam lenght
294,00 m
in elevation +503 masl, wide
catchment area 355 km2 and normal water level
at elevation +499,5 m and lowest water level
elevation +495,00 masl.
U
PLTA Upper Cisokan Dam development
Figure 1.Reasearch map location (not for scale)
Upper Cisokan Dam development take
places in upper Cisokan River that belongs to
Citarum Drainage System, West Java Pro vince
Indonesia.The main component of Upper Cisokan
Dam
are Upper Dam that take places in
Cirumanis River while the Lower Dam take
places in Cisokan River.
Upper Cisokan Power Plant development
head for supplying 1040 Megawatt to Java and
Bali.PLTA Plta upper cisokan can store energy at
the peak load , by pumping water from reservoirs
from upstream to downstream as the depositary of
energy and use excess energy at the base load ,it
can be benefits as providers of electric power at
the peak load, controled frequency, dynamic
response, serves as generating facilities stand by
Figure 2. Curve daily load with annual
maximum load
Figure 3. PLTA Cisokan works system
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10th Asian Regional Conference of IAEG (2015)
Figure 4. Layout of Construction Areas Upper and Lower Reservoirs (PT. PLN (Persero), 2010)
2. Methodology
Methodology consist of Literature study,
fieldwork, and laboratorium analysis. Literature
study done before fieldwork to collect secondary
data consist of DEM analysis and geological
region map quadrangle analysis. Fieldwork
consist collect field data, outcrop analysis,landuse
and actual erosion measurement.Lab analysis
consist of data processing to analyze relation
about geological factors, landuse and erosion
factor to know the potential erotion zone.
into two parts based on van zuidam ( 1985 ) ,
namely a steep slope 20 % -50 % dominant in the
east the study area occupies 48 % the study
areas .And the very very steep slope 50 % 140 % . Occupy 52 % of all research area.
Upper Dam
developement
Lower Dam
Developement
3. Result and Discussion
3.1 Geomorfological and Geological Setting
Morfography reasearch area shows
elevation between 400-1025 masl, according Van
Zuidam classification (1985) the morphology
consist of hill until high hill. Morfometri divided
Figure 5. Digital Elevation Model Map
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10th Asian Regional Conference of IAEG (2015)
Upper dam
developement
Lower dam
developement
( Not for scale )
Figure 6. Geological Reasearch area based on Geological of Cianjur Quadrangle Sudjatmiko 2003; Modified
Based on physiography the study areas
including into bogor zones and
southern
mountains zone.According to sudjatmiko
( 2003 ) in geological of Cianjur quadrangle
map, research area consist of three formations
namely Rajamandala formation,
Citarum
formation,and Jatiluhur formation. Geological of
Cianjur quadrangle map ordered from elder to
younger stratigraphy at the research area:
1. Clay, marl; quartz sandstones member of
Rajamandala formation
2. sandstone and marl member of Citarum
formation
3.
Basalt and breccia sandstone member of
Jatiluhur Formation
4. Pumice tuff and tuffaceous sandstone
5. Tuffaceous breccia, lava, sandstone and
conglomerate.
The existence of a structural geology in the
reasearch area consist of joint , fold and fault make
the research area has complexity in tectonic
history .A geological fault in meet the area will be
used as upper reservoir.This should be evaluated for
its harm in the construction of upper Dam reservoir.
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10th Asian Regional Conference of IAEG (2015)
3.2 Erosive Proses and Analysis
Upper dam
developement
Lower dam
developement
Figure 7 . Landuse map of reasearch area.
Code
Indicators
0
No roots are exposed; No crusting; No pedestal sprinkling; cover by vegetation more than
70% (Canopy and surface).
½
Little roots exposure; crusting; no pedestal sprinkling; soil on plants vegetation the upward
plants slope higher than ground; cover by vegetation 30-70 %
1
Roots exposure;pedestal sprinkling; ground covered by plants with 1 to 10 mm depth;
Little crastng, cover by vegetation 30 – 70 %.
2
Roots exposure dan sprinkling pedestal dan pile of the ground 5 cm; covered by vegetation
30 – 70 %.
3
Roots eksposure; sprinkling pedestal, pile of the ground with 5 - 10 cm depth, 2 – 5 mm
width krastng, grass in the lower slope covered by material washing product come from the
top slopes;cover by vegetation30 – 70 %
4
Roots exposure; sprinkling pedestal, pile of the ground 5 - 10 cm depth, coarse material
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10th Asian Regional Conference of IAEG (2015)
are exposure; rill erosion more than 8 cm depth; open field.
5
Trench Erosion (”gully erosion”), rill erosion more than 8 cm depht, open field.
Table 2. Parameter of erosion code and its idicators.
Erosion can be classified based on sign of
actual erosion such as rill erosion, a sheet erosion,
and gully erosion in the field , from the data we can
group into several codes and an indicator as
explained in table above based on the intensity of
erosion.Erosion in the study areas in general can be
classified into:
1. Very light erosion ( code 0 ). no roots exposure;
no krusting; no sparking pedestal; more than
70 % of the canopy and cover by vegetation,
consist of a steep slope ( 20 % to 50 % ) Occupy
4.8 % of all the research area..
2. Light intensity of erosion (Code ½ and 1) .The
roots exposure; krusting; spraking pedestal;the
upward plants slope higher than ground; the
ground covered by plants with 1 to 10 mm
depth; 30-70% average cover by vegetation,
with a steep slope (20% - 50%), occupy 2,55 %
of all research area.
3. Middle intensity of the erosion (Code 2 and
3).Roots exposure, sparking pedestal and a pile
of ground with the depth of 5 and 10 cm, the
thickness of krasting 2 – 5 mm, grass in the
lower slope covered by material washing
product come from the top slopes;cover by
vegetation30 – 70 %.A steep slope (20% 50%),occupy 20,33 % of all research areas.
4. Heavy intensity of erosion (Code 4 and 5).There
is no roots exposure; no krusting; there is no
sparking pedestal; Cover by vegetation less than
70% of the canopy, with a steep slope (20% 50%), dominant in the eastern research area
occupy 26, 7% percent of all research area.
Explaination :
Upper Dam
Developement
Pic a.
Lower Dam
Developement
Pic a. Very weak of erosion
intensity area
Pic b.
Pic b. Light of
erosion intensity area
Gambar 8. Erosion zone arround reasearch area
Pic c.
Pic d.
Pic f.
Pic e.
Pic e, f. Heavy intensity of erosion area, there is a
gully erosion
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Pic c, d. Midle of erosion
Intensity area
10th Asian Regional Conference of IAEG (2015)
3.3
“heavy use area” where animals are held to
protect pastures when soils are wet or plants
are recovering from grazing. For more
information, see the Horses and Livestock
section.
Erosion Prevention
Here’s a sampling of conservation practices
that can be used. They are more effective when
used in combination:
1. Filter strips and buffers slow water speed,
filter pollutants, and trap sediment. They can
be used to stop sediment from leaving the
farm. Grass filter strips are effective on
slopes less than 10 percent. Riparian buffers
of native trees and shrubs protect streams and
may be 40 to 300 feet wide, based on site
conditions and stream width.
2. Grassed waterways are flat-bottomed
channels planted with grass that are designed
to slow water down to prevent gulley
formation. Farm equipment can drive over
the side slopes during the dry season.
Waterways may need to be combined with
rock linings or drop structures on steep slopes.
3. Conservation tillage reduces the amount of
tillage and leaves at least 30 percent cover
from crop residue after harvest and during
winter months. Soil loss is reduced by 50
percent compared to bare soil.
4. Contour farming runs rows “on the level”
perpendicular rather than up and down the
slope. Crop rows form hundreds of small
dams that slow water and reduce soil loss up
to 50 percent.
5. Cover crops temporarily protect the soil until
the main crop is planted. Cover crops also
add organic matter and reduce weed growth.
Plant cereal grains and legumes for winter
cover crops. Buckwheat is a good summer
cover crop.
6. Pasture management balances livestock
numbers, forage, and water for a healthy farm
income and environment. Pastures with at
least 70 percent plant cover have little
erosion and produce more forage. Set aside a
5.
Acknowledgment, Appendix and References
Conclusion
Based on analysis above, the research area
consist of the sedimentary rocks and tuff material
with steep dipping in the fold and fault structural
geology area.Research area is susceptible to soil
erosion. An infertile soil condition make people to
open their agriculture, the opening field caused the
bad impact which the accelerated erosion can
endanger to the local residents and Upper Cisokan
development.The prevention can used some methode
such as filter strips and buffers slow water speed,
grassed waterways, soil conservation tillage, contour
framing, cover crops and pasture management. Based
on field observations, Upper Cisokan dam
development has high potential of erosion. It needs
well public participation, government and scientist to
prevent the occurrence of natural disasters that can
endanger life and can harm Upper Cisokan dam
development. Geological factor, steeply slope, high
rainfall intensity, and opening field can cause
accelerated erosion.The early prevention is needed to
minimize erosion.
Anknowledgement
On this chance the authors would like
thanks to Allah S.W.T for all of His Mercy and
grace, and people who have helped us in
preaparing and completing this paper Mr. Dicky
Muslim, Novian Triandanu, Agil Gemilang, and
Vilia
Yohana.
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10th Asian Regional Conference of IAEG (2015)
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Sudjatmiko. 2003. Geological of Cianjur
Quadrangle,West
Java
Province.
Bandung: Geological reaserch and
developement center.
Morgan, R.C.P. 2005. Soil Erosion and
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